The present invention relates to internal mold release systems which may be used in the preparation of reaction injected polyurethanes and polyurea foam articles. These internal mold release systems are particularly useful in manufacturing shaped resin components by the structural reaction injection molding process (SRIM), wherein a liquid stream of polyisocyanate is impingement mixed with at least one other stream containing active hydrogen-containing liquids, catalysts, fillers and the mold release systems and transferred to a heated metal mold. A glass mat, or a mat of other structural fibers, is placed into the mold prior to the impingement mixing of the components so that the obtained part is a reinforced composite. SRIM processes are used commercially to manufacture various articles where high strength and low weight are of importance. For example, SRIM processes are used to manufacture interior trim substrates for automobiles, such as door panels, package trays, speaker enclosures and seat pans.
Developments in the chemistry of the polymer systems used in SRIM have resulted in urethane and urethane-urea polymers which are sufficiently cured to be demolded within about 40-60 seconds after injection. SRIM equipment has also improved so that the mechanics of opening and closing the mold also require only about 30-40 seconds. Urethane polymers are excellent adhesives and bond tenaciously to metal making it necessary to utilize a release agent so that parts can be quickly and easily removed without damage or distortion.
External mold release agents have been used by applying the release agent to the surfaces of the mold. The molds must be completely covered with the release agent, generally by spraying a solution or an emulsion of a soap or wax thereon. This procedure requires 30-60 seconds and must be done at least after every one to five parts, thus increasing the part to part cycle time by as much as 50%. Additionally, this constant spraying often causes excessive mold release agent to build up on areas surrounding the mold surface or on the mold surface itself. In this instance, the mold must be periodically wiped off and/or cleaned by solvent or detergent wash. This experience is time consuming and costly for the part manufacturer.
Thus, it is clear that mold release agents or systems which could be included in the reaction systems themselves, i.e., internal mold release agents or systems, would be advantageous in eliminating such difficulties, increasing productivity and reducing part cost. Various internal mold release agents have been proposed in an attempt to solve these problems. For example, U.S. Pat. Nos. 4,546,154 discloses the use of 0.5-1.5 percent by weight of polysiloxane mold release agents in reaction injection molding systems for this purpose. However, such materials have been found to provide an insufficient number of releases to make their use acceptable commercially.
Certain acids, such as fatty acids and their esters are known to act as mold release agents. For example, U.S. Pat. No. 4,098,731 discloses the use of salts of saturated or unsaturated aliphatic or cycloaliphatic carboxylic acids containing at least eight carbon atoms and tertiary amines which do not contain amide or ester groups as release agents for polyurethane foam production. U.S. Pat. No. 4,024,090 discloses the use of internal mold release agents which are the esterification reaction products of polysiloxanes and monocarboxylic or polycarboxylic acids. U.S. Pat. Nos. 5,128,807, 4,058,492, 3,993,606 and 3,726,952 all also disclose the use of carboxylic acids or their derivatives as mold release agents. U.S. Pat. No. 4,130,698 discloses the use of esters of a fatty acid, such as glycerol trioleate, olive oil and peanut oil, as a processing aid. However, such systems have proven to be disadvantageous as they provide an insufficient number of releases, particularly in SRIM systems.
Accordingly, it can be seen that there is a need for internal mold release systems which provide a sufficient number of releases to make them suitable for widespread commercial use. Thus, it is an objective of the present invention to provide internal mold release systems which result in a significantly higher number of releases in comparison to known systems. It is a further objective of the present invention to provide internal mold release systems which are particularly suitable for use in SRIM systems.